It is known to use filters of the aforesaid type for venting or ventilating in the automobile industry (or in vehicles in general, this term meaning an automobile, a truck, a motorcycle or the like); these filters are associated for example with venting apertures of containers containing electrical or electronic parts (such as the lens or lighting or headlight units of motor vehicles) or mechanical parts (gear boxes, for example) where pressure has to be equalized between the interior of these containers and the external environment. These filters are also known to present a conformation or elements at least such as to limit water entry into said containers, said water being able to derive from rain or puddles or being able to derive from the washing of the vehicle or its engine. For example, a filter is known presenting a hollow tubular (elbow) bent conformation and shaped internally as a labyrinth to prevent or at least limit water access from the outside to the inside of the container via the tubular (venting) cavity of the filter.
Filters of the said type are also known using membranes of hydrophobic material associated with an internal conduit of the filter communicating with the container interior. Examples of these filters are those described in U.S. Pat. No. 5,914,415 and U.S. Pat. No. 5,522,769. In such filters of the state of the art and in particular in those described in the aforesaid US patents, the membrane is an element separate from the filter body and must be associated therewith by usually complex operations which require time and considerable care to prevent the membrane from breaking during handling. These operations are therefore costly.
For example, in U.S. Pat. No. 5,522,769 the hydrophobic membrane(preferably of polytetrafluoro ethylene) is inserted into a channel or seat lying transverse to a venting or passage conduit of the filter. The seat has a suitable diameter to securely contain the membrane. This known solution, in which the filter body has a substantially cap conformation and the venting conduit is rectilinear, is difficult to construct precisely because of the operations for coupling the membrane to the interior of the known filter body.
This latter also presents a rectilinear venting conduit which does not provide optimal protection to the container to which the filter is connected when this latter is subjected to a direct flow of liquid, such as that to which that part of a front headlight of a vehicle facing the engine may be subjected when this latter is exposed to washing with relatively high water pressure.
This lack of protection against water infiltration can also appear in the case of tightness tests to which motor vehicle headlights or lens units or lighting systems are subjected, tests during which a high pressure water flow strikes the headlight container to verify its tightness. Again in this case, the conformation of the filter venting conduit is not such as to adequately protect the filtering membrane from the pressurized liquid should this latter cause breakage of the diaphragm provided in U.S. Pat. No. 5,522,769 for protecting the hydrophobic membrane. In this respect, the diaphragm can protect the membrane if the filter is immersed in a liquid or if the liquid is able to directly strike the membrane, as stated in the prior patent. However in this latter, the liquid which could strike the membrane is not stated to be a liquid under pressure, as is clear from the example offered in the text of the prior patent, in which this liquid is stated to be oil which is accidentally poured onto the filter.
U.S. Pat. No. 5,914,415 also describes a filter provided with a hydrophobic membrane or water repellent film associated, for example by subsequent fusion, with the filter body which is formed of elastomeric material. The, film is finally protected by a cover cap fixed by pins (rigid with the cap) inserted into seats in the elastomeric body. The filter described in the prior patent is constructed as a plurality of parts assembled together, resulting in high costs and production times, together with constructional difficulties related to the operations of coupling the water repellent membrane or film to the elastomeric body and of coupling the cap to this latter body.